Figure 4-24.Using angle iron to cut bevels on steel plate.Figure 4-23.Typical gouging operation using a low-velocitycutting jet for better control of depth and width.more difficult. A preheat temperature of about 500°F isnormally satisfactory.When cutting cast iron, adjust the preheating flameof the torch to a carburizing flame. This prevents theformation of oxides on the surface and provides betterpreheat. The cast-iron kerf is always wider than a steelkerf due to the presence of oxides and the torch move-ment. The torch movement is similar to scribing semi-circles along the cutting line (fig. 4-22). As the metalbecomes molten, trigger the cutting oxygen and use itsforce to jet the molten metal out of the kerf. Repeat thisaction until the cut is complete.Because of the difficulty in cutting cast iron withthe usual oxygas cutting torch, other methods of cut-ting were developed. These include the oxygen lance,carbon-arc powder, inert-gas cutting, and plasma-arcmethods.GOUGING MILD STEELCutting curved grooves on the edge or surface of aplate and removing faulty welds for rewelding are addi-tional uses for the cutting torch. The gist of groovecutting or gouging is based on the use of a large orifice,low-velocity jet of oxygen instead of a high-velocity jet.The low-velocity jet oxidizes the surface metal only andgives better control for more accurate gouging. Byvarying the travel speed, oxygen pressure, and the anglebetween the tip and plate, you can make a variety ofgouge contours.A gouging tip usually has five or six preheat orificesthat provide a more even preheat distribution. Automaticmachines can cut grooves to exact depths, remove badspots, and rapidly prepare metal edges for welding.Figure 4-23 shows a typical gouging operation.If the gouging cut is not started properly, it is possi-ble to cut accidently through the entire thickness of theplate. If you cut too shallow, you can cause the operationto stop. The travel speed of the torch along the gougeline is important. Moving too fast creates a narrow,shallow gouge and moving too slow creates the oppo-site; a deep, wide gouge.BEVELING MILD STEELFrequently, you must cut bevels on plate or pipe toform joints for welding. The flame must actually cutthrough 2.8 inches of metal to make a bevel cut of 45degrees on a 2-inch steel plate. You must take this intoconsideration when selecting the tip and adjusting thepressures. You use more pressure and less speed for abevel cut than for a straight cut.When bevel cutting, you adjust the tip so the pre-heating orifices straddle the cut. Apiece of l-inch angleiron, with the angle up, makes an excellent guide forbeveling straight edges. To keep the angle iron in placewhile cutting, you should use a heavy piece of scrap, ortack-weld the angle to the plate being cut. Move thetorch along this guide, as shown in figure 4-24.ELECTRIC DRIVE CUTTINGTORCH CARRIAGEAn improvement over mechanical guides is an elec-tric motor-driven cutting torch carriage. The speed ofthe motor can be varied allowing the welder to cut todimensions and to cut at a specific speed. A typicalmotor driven carriage has four wheels: one driven by areduction gear, two on swivels (castor style), and onefreewheeling. The torch is mounted on the side of thecarriage and is adjusted up and down by a gear and rack4-17